Overdominance

Overdominance is an alternate term for heterozygote advantage, a condition in genetics where the phenotype of the heterozygote is fitter than the phenotype of either homozygote. The concept of overdominance has been used by plant breeders crossing inbred strains and selecting for desired characteristics. The theory that heterosis or hybrid vigor could be explained by heterozygote advantage became known as the overdominance hypothesis.
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See balancing selection. See also underdominance.